Yes, it blocks unpopular candidates.

Yes, it is appropriate to block presidential nominees, because if the person can be defeated by a filibuster, they were not popular enough to hold the position to begin with. The American public loves a filibuster. C-Span-2 loves the ratings, because, let's be honest, when else would you watch C-Span 2. Filibusters are a win for justice and entertainment.

Yes. All political tactics have their place

I think filibustering presidential nominees is a valid political tactic, only because all political tactics have their place and a time. I could see how filibustering could be non-constructive and tasteless, but I see it as a matter of tactics. If there were a nominee whom I was very opposed to, I would favor a filibuster. However, I have never encountered that situation but it is just hypothetical,